wl12xx: AP-mode high level commands

Add commands to start/stop BSS, add/remove STA and configure encryption
keys. Split the encryption commands "set key" and "set default key" into
AP and STA specific versions.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Reviewed-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>